When you open either a savings account or checking account at a bank and deposit money into those bank accounts that money is insured by the FDIC in the event the bank either fails or gets robbed.
So you can get your money back should that bank fail or be robbed.
Each person who has a bank account is insured for up to $250,000.00 for each checking account at each bank.
Most people don't have $250,000.00 in their checking or savings account but if you do you should never deposit or keep more than $250,000.00 in one bank account and should spread the amount out over different banks so that you'll be insured.